Be on the lookout for a new column in the next Pond Boss. Pond builder and bulldozer artist Mike Otto will begin writing a column dedicated to pond construction. One of his topics will be reconstruction.
In the meantime, here's a thought.
Anytime you can increase pond size by going up, do it that way. Raising the dam and/or spillway is the most cost efficient way to increase pond size.
When it comes to removing bottom soils, remember this...silt and soft soils are expensive to move, they usually have to be moved twice. Dragline or excavator brings soils out, bulldozer spreads the spoils. Twice moved, twice costs. And, you don't get a bigger pond.
Not raising the dam means digging a yard of dirt to get a yard of water. Not efficient. Not a good trade. I would certainly look at building another pond, and explore the costs to compare with cleaning out an older pond.

Teach a man to grow fish...
He can teach to catch fish...